Acute renal insufficiency is a devastating illness in elderly persons with a survival to discharge reported to be about 30 to 55%. Even among those with no-pre-existing renal disease, there are some who will subsequently require chronic dialysis. Among those persons with underlying chronic renal insufficiency, an acute insult to the kidneys may accelerate the progression toward the need for renal replacement therapy. In 1988, persons 65 and over comprised about 27% of the 150,000 patients in Medicare's End Renal Disease program, almost all of whom were on chronic dialysis at a cost to Medicare of approximately $32,000 per person per year. Several clinical conditions which are common in elderly populations including congestive heart failure, cirrhosis, and renal insufficiency require local synthesis of prostaglandins to maintain renal perfusion.. Numerous experimental studies have shown that a large proportion of patients with these conditions will suffer deterioration in renal function when exposed to any of a variety of nonsteroidal anti- inflammatory drugs (NSAIDS). Patients with these disorders are at risk from acute ischemic injury to the kidney when they take NSAIDs because these drugs inhibit prostaglandin production. NSAIDs are a common exposure in elderly populations, with about 13% on prescriptions NSAIDs at any given time, and close to 40% getting at least one prescription during a year's time. Despite the high exposure to these drugs and their known acute detrimental effects on renal function, little is known about the impact of these drugs on clinically significant renal disease in the elderly. We therefor propose to conduct a retrospective cohort study to estimate the incidence of hospitalization for acute renal failure among all persons aged 65 years and older enrolled in the Tennessee Medicaid program from 1987 through 1991; (point prevalence enrollment of about 83,000); the incidence of hospitalization for acute renal insufficiency among this same population who are current users of prescription NSAIDs; and the relative and attributable risks for acute renal insufficiency associated with prescription NSAIDs use in this population.